What is mean by tool offset

Tool Offset:-

           This is one off the main part of the CNC machine. This will an affect the job and part program .it will mansion the tool distance from machine zero and distance from the job.

Tool offset is used to compensate for the difference when the tool actually used differs from the imagined tool used in programming (usually, standard tool).

In this unit, there is no G code to specify tool offset. The tool offset is specified by T code.

Tool offset type:-

1.   Geometry offset method
2.   Wear offset method
3.    Work offset method Or Work shift ( G54 )

Tool Geometry Offset and Tool Wear Offset:-

Tool geometry offset and tool wear offset are possible to divide the tool offset to the tool geometry offset for compensating the tool shape or tool mounting position and the tool wear offset for compensating the tool nose wear.

Tool Selection:-

                        Tool selection is made by specifying the T code corresponding to the tool number.  Refer to the machine tool builder’s manual for the relationship between the tool selection number and the tool.

Example:-

         N50 T02        (Second number tool selection)

Tool wear offset:-

                    The tool path is offset by the X, Y, and Z wears offset values for the programmed path.   The offset distance corresponding to the number specified by the T code is added to or subtracted from the position of each programmed block. It’s called wear offset.

Tool geometry offset:-

With the tool geometry offset, the work coordinate system is shifted by the X, Y, and Z geometry offset amounts.  Namely, the offset amount corresponding to the number designated with the code is added to or subtracted from the current position.

Tool offset cancel:-

                   Offset is cancelled when T code offset number 0 or 00 is selected. At the end of the cancelled block, the offset vector becomes 0.

N1 X50.0 Z100.0 T0202; (Creates the offset vector corresponding to offset number 02)

N2 X200.0;

N3 X100.0 Z250.0 T0200; (Specifying offset number 00 deletes.)

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Machine Zero and Program Zero

During every machining operation, the CNC machine uses a series of numerical instructions sent by the part program to control movements along the axes. These programs require a starting point that accurately lines up the cutting tool and the workpiece.

Each CNC machine has a built-in location that is called machine zero. This point typically is located at the farthest positive direction along the X-, Y-, and Z-axes, and it cannot be changed by anyone after it leaves the original manufacturer. A cutting tool or a worktable can be moved to the machine zero position for the loading and unloading of parts.

In addition to machine zero, each part program sets a starting location called program zero. Unlike machine zero, the programmer selects the program zero for each workpiece. This location acts as the origin from which all the other dimensions are calculated during the program and it is usually located on the edge of a workpiece. The CNC machine then adjusts its calculations to accurately align the cutting tool with the workpiece.

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Coordinates for the Turning Center

Milling machines are normally used to machine cubic work pieces. However, manufacturers will use turning centers (shown in Figure 1) to shape the dimensions of cylindrical work pieces.

During turning operations, the work piece is held and rotated in a spindle. A non-rotating cutting tool is moved against the rotating part to remove material. Because the Z-axis is always parallel to the spindle of the machine, it no longer describes up and down motion of the cutting tool. Instead, the Z-axis now describes the back and forth motion of the tool along the length of the work piece, parallel to the spindle. The X-axis specifies the distance of the cutting tool from the center of the work piece. Figure 2 shows both the X- and Z-axes.
The X-axis position of the cutting tool determines the diameter of the cylindrical work piece. On the typical turning center, the Y-axis is not programmable. In theory, the Y-axis defines the tool height. However, because the tip of the tool must cut on the centerline of the part, the tool is almost always fixed at the same Y-axis location.

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Coordinates for the Horizontal Milling Machine

It is true that the axes of the vertical milling machine perfectly match the right-hand rule. However, not all CNC machines follow the same setup. Horizontal milling machines require a shift in the axes because the spindle of these machines is in a different location.

Figure 1 shows the basic setup of a horizontal milling machine. As you can see, the spindle is located on the side. Because the Z-axis must always be parallel to the spindle of the machine, the Z-axis is tilted to the side, as shown in Figure 2. The X-axis still describes motion to the left and right. However, the Y-axis now describes motion that is up and down.

It may seem that the coordinates of this machine no longer match the right-hand rule. However, if you were to tilt your hand to match the worktable, you will see that the axes still line up appropriately.

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How to select tool data in Mazak Matrix Machine

 How to select tool data

3 simple step you select Tool Data


1. Select the mode selection switch in manual mode

Mode Selection Switch 

 2. Press the left corner button in soft panel key

3. Press tool Data button

         
 See this is Tool Data display

Finish

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Mazak Integrex E-650 H

Offset
     1. How to select tool data
     2. how to enter the tool data
     3. How to take tool offset
     4. How to take work offset
      5.

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Welding And Allied Processes

Introduction:-

     welding is one of the material addition operations where components made by various processes are permanently joined together to obtain the desired configuration .other techniques of joined the components are brazing, soldering, mechanical joining   ( riveting ,bolting and keying ) and adhesive bonding. Here we shall consider only welding and some of the allied processes like brazing and soldering .
                             
                     In welding processes the components are joined permanently by coalescence. To obtain coalescence or permanent bonding , the surfaces to be welded together must come into intimate contact so that activities between atoms result in the formation of common metallic crystals.

                      when two atoms come sufficiently close to each other , an attractive force is excreted   between them . this interacting attractive force is negligible when the distance between these atoms ( inter-atomic distance ) is greater then few atomic spacings ( that is , a few angstroms ) . As the interatomic distance is decreased ,the attractive force increase rapidly ( figure ) .The atoms ,however , do not collapse because a repulsive force is manifested as the interatomic distance  decreases .These two forces interact and are equal in magnitude at the equilibrium interatomic distance .At the intersection point ( figure ). the slope of the repulsive force is always greater than that of the attractive force,resulting in a stable equilibrium .
 
                Thus if two metallic bodies are brought sufficiently close to each other ( less than a few angstroms apart ) , then they will adhere together due to a large attractive force. The resulting coalescence or formation of common metallic crystals joins the two bodies permanently. The process of joining metals in this manner has come to be known as welding .

Butt - Welded Pipe

      The formation of ideal metallurgical bond requires smooth and flat surface which are free from oxides , absorbed gases and other contaminants , and the metals should have single crystals with identical structure and orientation with no internal impurities. Such an ideal situation can never be achieved in practice and various techniques have been developed to overcome this impossibility so that welding may be achieved .For example smooth and flat surfaces can be obtained by melting the surfaces or through application of pressure. Similarly , contaminants can be removed by causing sufficient metal flow along the interface through heating or application of pressure so that they are able to squeeze out. Thus, two metallic surfaces can be brought into close proximity through the application of temperature and pressure .In fact , in welding processes a combination of temperature and pressure ranging from high temperature and no pressure , to high pressure and no heating is applied.

                         When high temperatures are used for welding , the metallurgical structure and quality of metal may get affected  by the heating and cooling  cycle. At high temperatures , most metals also get adversely aspects by the environment near the welding zone. These aspects should be considered by the designer before recommending the process to be used .

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Coordinates for the Vertical Milling Machine

The most recognizable coordinates can be found on the vertical milling machine. Imagine that you are standing in front of the machine and facing it. The coordinates of this machine follow the right-hand rule shown in Figure 1. As you can see in Figure 2, the X-axis describes left and right motion of the cutting tool, the Y-axis describes back and forth motion of the tool, and the Z-axis describes up and down motion.
Depending on the machine, either the cutting tool or the worktable will move during machining operations. The positive and negative directions on each axis always describe the motion of the cutting tool in relation to the worktable. If the cutting tool is the movable part, the positive directions follow the right-hand rule. However, if the worktable moves, the positive and negative directions are reversed. As shown in Figure 3, table movement to the left is actually a positive motion because it shifts the position of the cutting tool to the right of the table.

The right-hand rule matches a vertical machining center

Directions of positive and negative spindle movement on a basic mill.

. As a tool moves from rest (A) to the right (B), it travels in a positive direction along the X-axis. Table movement to the left (C) also moves the tool in a positive direction along the X-axis.

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Standard Axes Locations

The following are general guidelines that determine the location of coordinate axes on any given CNC machine:

The Z-axis is always parallel to the spindle of the machine.

The X- and Y-axes are always perpendicular to the spindle of the machine.

The X-axis normally describes the longer direction of travel on the machine, and the Y-axis describes the shorter direction of travel.

Keep in mind that the spindle is different for the machining and turning center. On the machining center, the spindle is the device that holds the rotating cutting tool, as shown in Figure 1. On the turning center, the spindle holds the rotating workpiece, as shown in Figure 2. The important thing to remember is that the spindle involves rotational movement. In the next few lessons, you will learn how these guidelines apply to each particular machine.

The spindle holds a cutting tool on a machining center.

The spindle holds a workpiece on the turning center

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Coordinate Standards for Machines

Without a doubt, the two most common CNC machines are the machining center and the turning center. A machining center is used to machine flat or angled surfaces, and a turning center is used to machine cylindrical parts. Figures 1 and 2 illustrate both of these machines.

CNC machines rely on the coordinate system to machine incredibly accurate dimensions. This requires a mapping of the coordinate system onto the dimensions of the machine. Imagine applying the right hand rule to a machine. Every CNC machine is programmed to recognize where the X-, Y-, and Z-axes are located on the machine itself.

The location of axes on any CNC machine is not a haphazard process. Each machine relies on Electronics Industries Association (EIA) standards that dictate the location of these axes.

A turning center is used to machine cylindrical parts

A machining center is used to machine flat or angled surfaces.

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Coordinate Standards for Machines

A turning center is used to machine cylindrical parts

A machining center is used to machine flat or angled surfaces

Without a doubt, the two most common CNC machines are the machining center and the turning center. A machining center is used to machine flat or angled surfaces, and a turning center is used to machine cylindrical parts. Figures 1 and 2 illustrate both of these machines.

CNC machines rely on the coordinate system to machine incredibly accurate dimensions. This requires a mapping of the coordinate system onto the dimensions of the machine. Imagine applying the right hand rule to a machine. Every CNC machine is programmed to recognize where the X-, Y-, and Z-axes are located on the machine itself.

The location of axes on any CNC machine is not a haphazard process. Each machine relies on Electronics Industries Association (EIA) standards that dictate the location of these axes.
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Rotational Axes

In addition to the movements on the linear X-, Y-, and Z-axes, tools and workpieces can also move along rotational axes. These rotational axes describe how a part tilts or rotates around a line defined by at least two points. The three rotational axes are the A-axis, B-axis, and C-axis, as shown in Figure 1. Each rotational axis corresponds to one of the linear axes. The A-axis rotates around the X-axis, the B-axis rotates around the Y-axis, and the C-axis rotates around the Z-axis.

Rotational movement can describe a workpiece that is turned to expose different areas of its surface for machining. Rotational movement can also describe the angle of the cutting tool. For complex parts, a cutting tool that is angled may allow it to machine hard-to-reach areas. Figure 2 shows a part that required tool movement on a rotational axis.

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Absolute Coordinates

Though incremental coordinates are used in certain operations, absolute coordinates dictate the movements of both tool and workpiece for most CNC machines.

With absolute coordinates, the origin is always in a fixed position. Each new location is calculated from this fixed origin instead of the previous location. Even if there is an error while reaching the current location, that error is corrected once the tool or workpiece moves to the next location. Figures 1 and 2 compare two blueprints that use incremental and absolute calculations.

To return to the driving example, absolute coordinates are similar to driving according to street names instead of counting street by street. The street names act as fixed reference points that prevent you from perpetuating a driving mistake if you miss a turning point.

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Incremental Coordinates

As a CNC machine works on a part, the machine guides either the cutting tool or the workpiece from one location to the next. Depending on the operation, a CNC machine will use either incremental coordinates or absolute coordinates to determine this movement.
FIgure 1 shows a blueprint with dimensions that reflect incremental coordinates. With incremental coordinates, a new location is calculated from the current position. Once the tool reaches the new location, it becomes the base for the next position. In other words, the current position always acts as the origin for the next position. If you were driving down the street, incremental directions would be similar to traveling three streets north, two streets east, one street north, etc.

A potential problem with incremental coordinates is that an error can be carried from one dimension to the next. Let’s say that, while driving, you missed a street. All the rest of your distances would be inaccurate, and you would have to correct your instructions to reach your final destination.

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Coordinates in Blueprints

                                               

                                    Every part that is made in the shop is originally designed on a computer or a blueprint drawing. In order to lay out the dimensions of a workpiece, a designer uses a coordinate system to describe the measurements of each dimension. Figure shows a blueprint drawing that contains these measurements.

Both blueprint drawings and CNC systems rely on these numerical coordinates to determine the location and size of workpiece dimensions. Every location is given a numerical value that places it within the three axes.

A CNC machine can only perform what it is programmed to do. Before a part is made on a CNC machine, a programmer takes the numerical dimensions of the blueprint and turns them into step-by-step instructions. The CNC machine then uses the coordinate system to perform these instructions, one after another, to make the part.

  Blueprints Pediatrics (Blueprints Series)

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Positive and Negative Directions

Figure 1. Each axis has a positive and negative direction.

Figure 2. The positive direction of the Y-axis points away, and the positive direction of the Z-axis points upward.

                                     Each axis line contains a range of numbers. The origin, or the center of the axis line, is always zero. Numbers are then counted as they move away from the center on each side of the axis. One direction is positive (+), and the other is negative (-).

Measurements taken to the right side of the origin along the X-axis line are generally considered to be positive, or +x, while measurements to the left of the origin along the X-axis are negative, or –x, as shown in Figure 1. The positive and negative directions work the same way for the Y- and Z-axes as well.

Figure 2 shows the box corner. The positive direction of the Y-axis points away and the positive direction of the Z-axis points upward.

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The Axes and Origin

                             

An effective way to picture the three Cartesian axes shown in Figure 1 is by learning the right-hand rule. Turn your right palm up, and then extend only the thumb and forefinger. This forms an "L," with the middle finger up to the ceiling, as in Figure  The thumb is the X-axis, the forefinger is the Y-axis, and the elevated center finger is the Z-axis.
                                      The point where all three axes meet is called the origin. This occurs roughly in the palm of your hand, or the corner of the box. The origin is important because it is the central reference point for all the dimensions. You can think of the origin as the "You are here!" dot on a map. Within the Cartesian system, any specific location can be described by its place along the three axes and the distance from the origin.

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